The present invention relates to improvements in methods and apparatus for making bags by a form fill process wherein the bags have a reclosable fastener at the top. In the vertical form fill process, a length of plastic film is led downwardly over a tube with the lateral edges brought together and seamed to form a side seam, a cross-seam is created to form the bottom of a bag and contents are normally dropped in the bag through the tube about which the film is formed.
In the process of making reclosable bags that have a pressure closable fastener at the top, this fastener must be secured to the bag material in such a manner so that it is located at the top of the bag. The type of fastener to which the present invention relates is one which has interlockable rib and groove profiles. Where the bags are made of a thin film, these profiles are conveniently formed in strips of separate material. In this manner, the film of the bag can be made of a thin lightweight tough plastic having physical characteristics best suited for the bag. The fastener can be made of a different plastic having physical characteristics best suited for the fastener. The fastener is attached to the bag material by suitable means such as by adhesive or by heat sealing, and where both members are of plastic, the form of heat sealing attachment is particularly well suited for rapid operation and a secure joining between the fastener and the film of the bag material.
In a suitable manufacturing process wherein a series of bags are formed from a continuous supply of film, it is, of course, desirable that the machine can be operate at relatively high speed. Formation and filling of the bag involves drawing the film down over a vertical tube, forming the film into tubular shape, creating a side seam where the edges of the film are brought together and creating a bottom seam. The contents of the bag are then dropped through the tube and the tube drawn down whereupon the top is closed such as by pressing the rib and groove profile elements together to interlock them. The arrangement for providing the fastener strips on the inner surface of the bag wall is that the top of the bag creates difficulty in the high speed machine. One manner of attaching such fasteners has been to provide a continuous fastener strip across the film wherein the fastener strip has a plurality of ribs and grooves so that it can be folded on itself and the folded edge of the strip shifts so that the ribs enter the grooves. The difficulty with this arrangement is that this type of fastener strip often does not seal completely at the end and requires more plastic than the more simple rib and groove fastener. Other arrangements have been attempted which encounter difficulties and are not completely satisfactory.